Phylogenetic relationships among the New World cypresses (Hesperocyparis; Cupressaceae): evidence from noncoding chloroplast DNA sequences

Abstract

Nearly 5.6 kb of noncoding chloroplast DNA sequence was combined with 9.2 kb of previously published sequence in addressing phylogenetic relationships among Callitropsis, Xanthocyparis, and the New World cypresses (Hesperocyparis; Cupressaceae). Maximum likelihood and Bayesian analyses of aligned nucleotide sequence and coded length mutations provide strong support for several relationships. These include a clade in which Xanthocyparis and Callitropsis are successively nested at the base of a monophyletic Hesperocyparis and identification of H. bakeri as sister to the remaining Hesperocyparis. Two principal clades are recovered within Hesperocyparis; (1) the Arizonica group, which contains taxa sometimes recognized as varieties of H. lusitanica, H. guadalupensis, and H. arizonica, and (2) the Macrocarpa group, which contains H. macrocarpa and H. goveniana and its allies. Our results are equivocal with respect to placement of H. macnabiana, a morphologically distinct species resolved as the sister group to either the Macrocarpa or Arizonica group, depending on the data set analyzed. We discover many instances in which taxa recognized as varieties or closely related species are placed in disparate parts of the phylogeny. These include segregates of H. lusitanica, H. guadalupensis, and H. arizonica, all of which are included in clades with other species. Despite analyzing 14,799 bp of aligned sequence and 230 binary characters, we find poor support for several relationships, especially within the Arizonica group. These results suggest recovery of well-supported relationships among the closely related taxa of Hesperocyparis will require additional sources of evidence (e.g., morphological, biochemical characters). Implications for morphological evolution and taxonomic revision are discussed.